<canvas id="canvas" width="100" height="100"></canvas>
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
ctx.fillStyle = '#000';
ctx.arc(50, 50, 25, 0, Math.PI * 2, true);
ctx.fill();
ctx.filter = 'drop-shadow(0px 10px black)';
ctx.globalCompositeOperation = 'source-in';
ctx.fillStyle = '#0f0';
ctx.fillRect(25, 25, 50, 40);
</script>
